Because any modern unemployment insurance program (which Ireland has) will be a percentage based on salary. Struggling artist aren't exactly making regular money like a formerly employed salesperson or carpet installer would be.
I'm not in Ireland but it's the same everywhere. No one likes paying taxes.
Not saying that anything should be done about it. TBH I'd even like to have unemployment benefits be an optional insurance to reduce my taxes since I haven't gotten a cent out of it yet, but that's separate.
Just noting that artists aren't in some unique situation.
Nothing is stopping them from opening a company and giving themselves a fixed salary or doing some mix of salaried, freelance and under-table work.